1. Field of the Invention
The present invention relates to a retransmission control method and the apparatus in a base station for performing retransmission control for a signal sent from a mobile station.
2. Description of the Related Art
Conventionally, a method of sending acknowledgment is usually adopted as a retransmission control method in communication systems. In this method, when a receiver receives a signal which is sent from a sender, the receiver judges whether the signal is correctly received, that is, whether the signal includes an error. When the signal is correctly received, the receiver sends ACK (acknowledgement) which indicates that retransmission is unnecessary to the sender. When the signal is not correctly received, the receiver sends NACK (negative acknowledgement) for requesting retransmission to the sender. When the sender receives NACK, the sender retransmits a signal corresponding to the previously transmitted signal.
This retransmission control method is also adopted in a communication system in which mobile stations and base stations communicate each other via communication channels. For example, as far as retransmission control for a signal sent from a mobile station to a base station (which will be called an up-link signal hereinafter) is considered, an mobile station which plays a role of a sender sends a signal to a corresponding base station with which the mobile station communicates, that is, a communication partner of the mobile station. The base station performs error judgment for the received up-link signal. When there is an error in the received signal, the base station sends NACK to the mobile station. On the other hand, when there is not any error, the base station sends ACK to the mobile station. When the mobile station receives NACK, the mobile station retransmits a corresponding up-link signal.
In the above-mentioned communication system in which an up-link signal from a mobile station is received by one or more base stations other than a corresponding base station with which the mobile station communicates, there is a case in which a base station adjacent to the corresponding base station correctly receives the signal even when the corresponding base station does not correctly receive the signal.
However, in the conventional retransmission control method, when the corresponding base station judges that the up-link signal includes an error, the corresponding base station sends NACK to the mobile station even if other base station correctly receives the signal. Such inefficient retransmission control increases load for retransmission process. In addition, such retransmission control becomes a factor for preventing effective use of communication channels.